THE MENDIPS : A GEOLOGICAL REVEKIE. 



239 



and perliajia oxtendiug to tlie present coast of Norway. 

 Another, Lake Caledonia, occupied tlie central valley of 

 Scotland, and spread thence to the north of Ireland. 

 Smaller lakes occupied the site of the Cheviots and of 

 northern Argyllshire. 



Not only were there groat lakes in Scotland at the time 

 of which I speak, Init this region was also one wherein vast 

 volcanoes poured Ibrtli immense streams of lava, which 

 flooded the country and were interbedded with the sand- 

 stone and other deposits tliat were being swept piecemeal 

 by rivers and streams into the basins of the Scottish lakes. 

 By these deposits, volcanic and other, the lakes were to a 

 large extent silted up. But it would seem that elevation 

 of the country also took place, and the lakes may have been 

 drained of their waters by the deepening of the valleys 

 through which their efiiuent rivers flowed seawards. The 

 country would then have presented " the aspect of a high 

 and dry upland formed of lofty hill-ranges, separated by 

 immense plains, the sites of the desiccated lakes." But 

 this state of things was not to last. " A reverse movement 

 at length set in toward the end of the Devonian pei-iod ; 

 portions of the old lake-basins were again lilled with water, 

 the area of which widened and deepened as the land sank ■ 

 torrents washed in the detritus of the land, and the 

 material tlius collected became the conglomerates and sand- 

 stones of the upper old red. and lower carboniferous series " 

 (Jukes-Browne). 



fuller investigation. In the iireparation of the succeeding maps, with 

 the exception of that of the Mendip Isle, for which I alone am respon- 

 sible, I have been aided by Mr. A. J. Jukes-Browne, whose forthcoming 

 volume on " The Building of the British Isles," some of the proof-sheets 

 of which he has, with great courtesy and kindnes.s, allowed me to see, 

 will form a most interesting and valuable contribution to the palmo- 

 geography of our islands. 



